Water-Soluble Ruthenium(II) Carbonyls with 1,3,5-Triaza-7-phosphoadamantane

As a continuation of our strategy for preparing new Ru­(II) precursors with improved water solubility through the introduction of highly water-soluble 1,3,5-triaza-7-phosphoadamantane (PTA) supporting ligands in the coordination sphere, in this work, we address the largely unexplored preparation of Ru­(II)–PTA carbonyls. Two complementary synthetic approaches were used: (1) the treatment of a series of neutral Ru­(II)–CO–dmso compounds of general formula RuCl₂(CO)_<i>n</i>(dmso)_4–<i>n</i> (<i>n</i> = 1–3, <b>1</b>–<b>5</b>) with PTA; (2) the reaction of Ru­(II)–PTA complexes with CO. Through the first approach, we obtained and fully characterized seven novel neutral compounds bearing from one to three PTA ligands per Ru atom, namely, the four monocarbonyls, <i>cis</i>,<i>cis</i>,<i>trans</i>-RuCl₂(CO)­(dmso–S)­(PTA)₂ (<b>6</b>), <i>trans</i>-RuCl₂(CO)­(PTA)₃ (<b>7</b>), <i>cis</i>,<i>mer</i>-RuCl₂(CO)­(PTA)₃ (<b>8</b>), and <i>trans</i>,<i>trans</i>,<i>trans</i>-RuCl₂(CO)­(OH₂)­(PTA)₂ (<b>10</b>), and the three dicarbonyls, <i>trans</i>,<i>trans</i>,<i>trans</i>-RuCl₂(CO)₂(PTA)₂ (<b>11</b>), [RuCl₂(CO)₂(PTA)]₂ (<b>12</b>), and <i>cis</i>,<i>cis</i>,<i>trans</i>-RuCl₂(CO)₂(PTA)₂ (<b>13</b>). The less stable, and thus more elusive, species <i>fac</i>-RuCl₂(CO)­(PTA)₃ (<b>9</b>) and <i>cis</i>,<i>cis</i>,<i>cis</i>-RuCl₂(CO)₂(PTA)₂ (<b>14</b>) were also unambiguously identified but could not be obtained in pure form and fully characterized. The complementary synthetic approach, that involved the treatment of the <i>trans</i>- and <i>cis</i>-RuCl₂(PTA)₄ (<b>15</b>, <b>16</b>) isomers with CO, afforded only one new Ru­(II)–PTA carbonyl, the cationic species <i>cis</i>-[RuCl­(CO)­(PTA)₄]Cl (<b>17</b>). In general, the choice of the solvent was very relevant for obtaining the products with high yield and purity. We were unable to isolate Ru­(II)–PTA compounds with more than two carbonyls. The thermodynamically preferred species have CO <i>trans</i> to Cl and two mutually <i>trans</i> PTAs, and only in the dinuclear compound <b>12</b> there is a single PTA per Ru atom. Compounds <b>7</b> and <b>17</b> feature the unprecedented <i>trans</i>-{Ru­(CO)­(PTA)} fragment. The X-ray structures of <i>cis</i>,<i>cis</i>,<i>cis</i>-RuCl₂(CO)₂(dmso)₂ (<b>3</b>), <b>6</b>–<b>8</b>, <b>10</b>, <b>11</b>, <b>13</b>, and <b>17</b> are also reported. All compounds are new, are air-stable, and show a good solubility in water (<i>S</i> from 10 to 165 g·L^–1) and, most often, also in chloroform